Image capture devices, such as digital video cameras or digital still photo cameras, are used in different applications and environments. An image capture device should be capable of producing high quality imagery under a variety of lighting conditions. For example, image capture devices should be capable of operating effectively in environments illuminated by natural light, such as outdoor environments, as well as in environments illuminated by incandescent or fluorescent lights, such as indoor environments.
In an indoor environment, however, fluctuations in the intensity of indoor lighting can degrade the quality of the captured image. The fluctuations are a function of the alternating current (AC) electrical power frequency of the indoor lighting source. A solid state image capture device, such as a complementary metal oxide semiconductor (CMOS) device, includes an array of image sensors that do not instantaneously capture all of the image information used to record a frame. Consequently, fluctuations in light intensity during image capture cause portions of an image frame to exhibit different intensity levels, resulting in visible bands in the image. This banding phenomenon is commonly referred to as flicker.
Flicker may be eliminated by setting the integration time of the image capture device to an integer multiple of the period of the illumination source. The integration time refers to the time limit for the sensor array to capture light for each frame. Typically, flicker is more severe for shorter integration times. Variations in the AC power frequency of indoor lighting exist throughout the world. Some countries use 60 Hertz (Hz) power, for example, while other countries use 50 Hz power. A 60 Hz illumination source causes banding at 120 Hz, while a 50 Hz illumination source causes banding at 100 Hz. Some countries use both 50 and 60 Hz AC power, even within the same building in some instances.
Flicker may occur when the image capture device is used in an environment in which the illumination source is operating at a frequency other than an anticipated frequency. For instance, if the integration time of the image capture device is set as an integer multiple of the period of a 60 Hz illumination source, flicker can occur when capturing imagery in a 50 Hz illumination environment, and vice versa.